[m-users.] A naming and access problem

[Sean Charles (emacstheviking)]

Yes that was line 199 and arg/4 is

    % arg(Data, NonCanon, Index, Argument)
    %
    % Given a data item (Data) and an argument index (Index), starting
    % at 0 for the first argument, binds Argument to that argument of
    % the functor of the data item. If the argument index is out of range
    % -- that is, greater than or equal to the arity of the functor or
    % lower than 0 -- then the call fails.
    %
    % Note that this predicate only returns an answer when NonCanon is
    % do_not_allow or canonicalize.  If you need the include_details_cc
    % behaviour use deconstruct.arg_cc/3.
    %
:- some [ArgT] pred arg(T, noncanon_handling, int, ArgT).
:- mode arg(in, in(do_not_allow), in, out) is semidet.
:- mode arg(in, in(canonicalize), in, out) is semidet.
:- mode arg(in, in(canonicalize_or_do_not_allow), in, out) is semidet.




> On 18 May 2021, at 12:36, Volker Wysk <post at volker-wysk.de> wrote:
> 
> Am Dienstag, den 18.05.2021, 09:00 +0100 schrieb Sean Charles
> (emacstheviking):
>> Hi, I have a token definition like this:
>> 
>> :- type location
>>           ---> pos(index::int, line::int, col::int).
>> 
>> % for ast detection later.
>> :- type token
>>           ---> tk(location, string)
>>           ; '('(location) ; ')'(location)
>>           ; '['(location) ; ']'(location)
>>           ; '{'(location) ; '}'(location)
>>           ; c1(location, string) ; cn(location, string)
>>           ; s1(location, string) ; s2(location, string)
>>           .
>> 
>> Given the above, I have now realised that I can’t easily (?) access the location part of any particulr instance of the token type because it doesn’t have a name and thus no field reader will be generated. As I understand it, I would have to give a unique name.
>> 
>> I tried:
>> 
>>    arg(Tok1, canonicalize, 0, Out),
>> 
>> and was rewarded with this message from the compiler,
>> 
>> repl.m:199: In clause for predicate `run_lex'/3:
>> repl.m:199: in argument 1 of call to predicate `lexer.on_string'/4:
>> repl.m:199: in argument 2 of functor `string.between/3’:
>> repl.m:199: in unification of argument
>> repl.m:199: and term `index(Out)’:
>> repl.m:199: type error in argument of functor `index'/1.
>> repl.m:199: Argument 1 (Out) has type `(some [ArgT] ArgT)’,
>> repl.m:199: expected type was `lexer.location’.
>> 
>> Which is fair enough but how do I do it? That message is currently above my pay grade.
>> Have I overlooked something blindingly obvious?
> 
> Is that "arg(Tok1, canonicalize, 0, Out)" the line 199? There isn't any term
> "index(Out)". What's the declaration of arg/4?
> 
> Volker

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